[`pyflakes`] Show syntax error message for `F722` (#15523)
## Summary
Ref: https://github.com/astral-sh/ruff/pull/15387#discussion_r1917796907
This PR updates `F722` to show syntax error message instead of the
string content.
I think it's more useful to show the syntax error message than the
string content. In the future, when the diagnostics renderer is more
capable, we could even highlight the exact location of the syntax error
along with the annotation string.
This is also in line with how we show the diagnostic in red knot.
## Test Plan
Update existing test snapshots.
